BAGHDAD – It was supposed to be a routine job, police say. Move 69 prisoners from an outlying town to a jail in southern Baghdad. But before they arrived at their destination, every single prisoner had been killed.

The official account given hours after the killing on Monday by the governor of Hilla, 92km (57 miles) south of Baghdad, was that militants had attacked the convoy killing 10 prisoners and one policeman in the crossfire.

But a police captain, a second police officer and a senior local official from where the prisoners died in Hilla, all speaking on condition of anonymity while giving an account that differed from the official line, told Reuters no attack took place, and the police had executed the 69 men.

A third police source who would not contradict the account that the convoy had come under attack nevertheless confirmed that all 69 had been killed and said some had not died in the crossfire but were gunned down to prevent them from escaping.

The deaths in Hilla came less than a week after the killing of 52 prisoners in Baquba, a regional capital north of Baghdad.

The police account there also was that the prisoners had died in the crossfire during a battle with insurgents. But local Sunni officials including the mayor and the provincial governor, medical staff at the morgue and relatives of the dead all said the victims were gunned down in their jail cells.

Iraq's government has long denied it summarily executes prisoners. Following a Reuters report on police executions in March, army spokesman Sa'ad Ma'an said: "If it happened, whoever committed it will be investigated, held accountable and sent to a military court."

Ma'an and other Iraqi government spokesmen did not respond to repeated requests for comment on the latest killings outside Hilla.

Unlike the Iraqi government, Sunni insurgents from the Islamic State in Iraq and the Levant make no attempt to hide mass executions of prisoners: they proudly proclaim that Shi'ites are heretics who must die, and boast of the killings.

Days after they began sweeping through northern cities on June 10, they released videos showing their masked fighters machine gunning captive government soldiers lying in shallow graves. On Friday, Human Rights Watch said ISIL had executed at least 160 people in Tikrit this month.

But the reports that government forces loyal to Prime Minister Nuri al-Maliki are also executing prisoners are becoming more regular as the conflict intensifies, calling into question Washington's stepped-up military support for the Shi'ite premier.

PRE-EMPTION

Several police sources interviewed by Reuters said prisoners were being preemptively killed in Iraq to prevent militant groups from freeing them to rejoin the rebellion.

"We feed them and keep them healthy and if the ISIL managed to free them, they will immediately resume fighting us," the police captain who acknowledged the executions in Hilla said.

"We have to defend ourselves by executing those criminals."

The second Hilla police officer said summary executions were routinely carried out by army and police forces.

"First thing we do is to shoot them in foot and then take their confessions. Then we kill them and write in report they were killed in action," he said, also on condition of anonymity.

The third police officer, who denied that the Hilla prisoners were executed, nevertheless said the reason some of the 69 had been shot was to prevent them from escaping. He said the convoy had been hit by a roadside bomb and came under fire.

"We are not an execution squad. What happened was that we were trying to transport high-profile, dangerous members of al Qaeda - most of them awaiting death sentences - to another secure detention centre south of Baghdad," he said.

"The convoy came under attack by militants who set off two roadside bombs. Some of the prisoners wanted to use the attack to escape. We shot them dead as they were escaping."

A senior local official in Hilla said the attack on the convoy had been staged to hide the execution.

"The police brought the bodies of 16 other terrorists they had executed earlier to the scene and laid weapons by their corpses to pretend they had attacked the convoy," he said.

ISIL ATTACKS

One of ISIL's main aims is to free Sunni prisoners from government jails, and Iraqi police and troops who guard them come under frequent attack.

A year ago ISIL launched its biggest military operation in years, attacking two jails. Hundreds of convicts, including senior members of al Qaeda, were freed from Abu Ghraib jail on Baghdad's western outskirts in the assault, which saw suicide bombers blast through the gates.

When militants took Mosul city on June 10 at the start of their present offensive, they freed as many as 1,000 prisoners from a jail.

The government's harsh justice towards prisoners did not begin with this month's ISIL advance, however.

In a Reuters investigation in March, a police officer, an army officer, a general and an Iraqi Special Forces member all said that in western Anbar province Iraqi troops had begun replying in kind to ISIL, carrying out extra-judicial executions, torture and humiliations of their enemy and posting images of the results online.

On June 4, a week before the assault on Mosul, the chief of police in Hilla held a news conference to display six captives, charged with a car bomb attack that killed 14 people. The prisoners confessed in front of cameras to having bombed Hilla hospital.

Hours later, Police Chief Major General Riad al-Hikani posted pictures of the bullet-riddled bodies of four of the suspects on his Facebook page.

He said they had been killed when unidentified assailants opened fire while they were being escorted to cells, but expressed no regret at the death of captives in his custody.

"Delighted that divine justice has been achieved against them," Hikani wrote on Facebook.